Ultra low density cementitious slurries for use in cementing of oil and gas wells

ABSTRACT

The storable, low-density, hydraulically-active, cementitious slurry of the invention is suitable for cementing within a subterranean formation for oil or gas wells. The low-density slurry comprises a hydraulically-active cementitious material, a set retarder, a plasticizer, glass or ceramic micro-spheres, and a strengthening agent. Further the slurry is substantially free of a suspension agent. The storable, low-density, hydraulically-active, cementitious slurry is made by adding glass or ceramic micro-spheres to a hydraulically-active cementitious material, adding a strengthening agent to the microsphere containing composition, and mixing the resulting composition with water, a set retarder, and a plasticizer to generate a slurry, wherein the set retarder is present in an amount sufficient to allow storage of the slurry.

This application claims the benefit of U.S. patent application Ser. No.10/646,147 filed on Aug. 22, 2003.

FIELD OF THE INVENTION

This invention relates to ultra low density storable cementitiousslurries useful for oil and gas well cementing, as well as to a methodof cementing an oil or gas well using such slurries. Such cementitiousslurries are further useful in the zonal isolation of subsurfaceformations.

BACKGROUND OF THE INVENTION

Hydraulic cements are cements that set and develop compressive strengthdue to a hydration reaction, not drying. Thus, hydraulic cements can setunder water. Consequently, hydraulic cements are often used forcementing pipes or casings within a well bore of a subterraneanformation for the construction of oil, gas and water wells, as well asother purposes, such as remedial squeeze cementing. In the oil and gasindustry, successful cementing of well pipe and casing during oil andgas well completion requires cement slurries to exhibit a pumpableviscosity, fluid loss control, minimized settling of particles and theability to set within a practical time.

Conventional mixing equipment is relatively complex and expensive sinceit must permit the addition of water to dry cement powder,homogenization of the mixture, measurement of its density and, ifnecessary, recirculation of the mixture. Such requirements furtherdictate the equipment's configuration. In addition, dry cement bulktransport equipment must usually be pressurized so that solids can betransferred pneumatically at relatively high rates to the cement pump.Once at the drilling site, the pneumatically conveyed cementing solidsmust be correctly proportioned and mixed with water, as well as otheradditives to form a pumpable slurry. The slurry must then be tested forthe appropriate density to verify correct solids to water ratio. Ifcementing solids are not correctly proportioned, the quality of thecement diminishes.

It is sometimes necessary to use a lightweight cement when there is aweak subterranean formation. A lightweight cement exerts a lowerhydrostatic pressure on the formation than do regular cements. Thelightweight cements should be lower in density without sacrificingstrength. The density can be lowered in these cements by either addingsealed microballoons or creating a foam by injecting the cement with agas, such as nitrogen. This foaming operation can be difficult becauseadditional nitrogen equipment is required and the addition of gas mustoccur onsite which requires that the density of the slurry be carefullymeasured before use. Methods of measuring the density as the cement ismixed are known. Such methods can be an inaccurate means of cementsolids to water ratio verification—when the density of the cementapproaches the density of water, making differentiation between cementand water difficult.

Low density cements have been used previously. For example, thesecements have been disclosed in U.S. Pat. Nos. 4,370,166 and 4,234,344.These patents disclose the use of inorganic material in order to lowerthe ultimate density of the cement. However, the difficulty with thesedisclosures, and other conventional cementing slurries, is that they setquickly and therefore cannot be made in advance of their use. A delay inthe drilling operation delays the cementing job. If personnel andequipment for cementing idly wait onsite until the drilling ends, adelay can increase the cost of the cementing job. A slurry made inadvance and stored until needed would allow the personnel and equipmentto make the storable slurry, regardless of whether drilling had ceasedor even begun.

Storable cementitious slurries have been made in the past. Examples ofthese attempts are demonstrated in U.S. Pat. Nos. 5,447,197; 5,547,506;and 6,173,778. These patents, however, do not disclose the use of lowdensity slurries in a storable form.

Therefore, there is a need to create an ultra low-density, storable,slurry capable of being used in cementing a well formation.

SUMMARY OF THE INVENTION

The storable, low-density, hydraulically-active, cementitious slurry ofthe invention is suitable for cementing within a subterranean formationfor oil or gas wells. The low-density slurry comprises ahydraulically-active cementitious material, a set retarder, aplasticizer, glass or ceramic micro-spheres, and a strengthening agent.Further the slurry is substantially free of a suspension agent. Use ofsuch slurries in oil or gas wells helps to establish zonal isolationwithin the cemented wellbore of the subsurface formations.

The storable slurry of the present invention allows the density of thecement to be pre-determined and accurately measured before thecementitious slurry is shipped to the wellsite. This in turn, can reduceup-front cost for mechanical equipment such as foam generators andassociated nitrogen pumps and storage vessels.

Further, this invention establishes an alternate means to accurately mixand place ultra-low density cement systems without the use ofconventional continuous mix cementing equipment or foam and itsassociated equipment.

Further, this invention allows the reduction and/or elimination oftypical and auxiliary cement mixing equipment and material on locationsuch as cement pumps, nitrogen tanks and pumps and the personnelnecessary to operate this equipment.

Further, the accurate control of the premixed slurry propertieseliminates job uncertainties and leads to a significant improvement inQA/QC.

This invention allows the cementing of a subterranean formation using alow density cementitious slurry after it has been stored for a period oftime. It further provides a low-density storable cement slurry that canbe made at a different location from the job site. This storable slurrycan then be transported to the job site before cementing.

The storable, low-density, hydraulically-active, cementitious slurry ismade by adding glass or ceramic micro-spheres to a hydraulically-activecementitious material, adding a strengthening agent to the microspherecontaining composition, and mixing the resulting composition with water,a set retarder, and a plasticizer to generate a slurry, wherein the setretarder is present in an amount sufficient to allow storage of theslurry wherein the slurry is substantially free of a suspension agent.

In one method of the invention, a subterranean formation for an oil orgas well is cemented with the storable, hydraulically-active,cementitious slurry formulated by mixing together a hydraulically-activecementitious material with a set retarder, plasticizer, glass or ceramicmicro-spheres, and strengthening agent, wherein the storable slurry'scharacteristics remain within usable parameters during storage. Thestorable slurry is then stored until required for cementing, at whichtime it is activated by mixing together an activator with the storableslurry, pumped into the subterranean formation and allowed to set.

In another method of this invention the steps of the method of cementingthe subterranean formation are performed at two different locations. Inthis method the stable, low-density, hydraulically-active, cementitiousslurry is formulated at one location, transferred to a second location,activated at the second location, and then pumped into the subterraneanformation for cementing.

Additional effects, features and advantages will be apparent in thewritten description that follows.

DETAILED DESCRIPTION OF THE INVENTION

A storable, hydraulically-active, cementitious slurry of the inventionis made from a hydraulically-active cementitious material. Thecementitious systems of the invention allow for the zonal isolation ofwellbores. The cementitious slurries exhibit ultra low-densities,typically ranging from about 13.0 pounds per gallon (ppg) to about 6.0ppg or less, preferably from about 10.0 ppg to about 8.0 ppg.

Hydraulically-active cementitious materials include materials withhydraulic properties, such as hydraulic cement, slag and blends ofhydraulic cement and slag (slagment) which are well known in the art.The term “hydraulic cement” refers to any inorganic cement that hardensor sets due to hydration. In this disclosure, the term“hydraulically-active” refers to properties of a cementitious materialthat allow the material to set in a manner like hydraulic cement, eitherwith or without additional activation. Hydraulic cements, for instance,include Portland cements, aluminous cements, pozzolan cements, fly ashcements, and the like. Thus, for example, any of the oilwell typecements of the class “A-H” as listed in the API Spec 10A, (22nd ed.,January 1995 or alternatively ISO 10426-1), are suitable hydrauliccements. This also includes Commercial Lightweight cement and ASTMconstruction cements.

The type of slag used for the invention has hydraulic properties. Theslag is preferably ground-granulated blast furnace slag with a minimumglass count of about 95% and a fine particle size of about 1 to about100 μm, preferably less than about 45 μm, most preferably less than 10μm or a fineness of about 310 to about 540 m²/kg. See, e.g., U.S. Pat.Nos. 5,125,455 and 5,106,423. A slag slurry develops little strengthwithout increasing the alkalinity of the slurry to initiate hydration.Slag alone can also produce a brittle set product and fluid loss fromthe slag slurry can be difficult to control.

Slagments are preferably blends of slag and portland cement. Examples ofsuitable slagments include blends ranging from about 90% cement with 10%slag to 10% cement with 90% slag, with a particularly preferred blend of60% slag with 40% cement with all percentages based on the dry weight ofeach component.

Slagment and hydraulic cement are preferred cementitious materials.However, both of these materials react quickly with water and set atroom temperature unless modified, and they are, therefore, much moredifficult to control. However, storable slurries formed from hydrauliccement, especially portland cement, or slagment have the best overallperformance characteristics for well cementing applications.

Hydraulically-active cementitious materials may also have minor amountsof extenders such as bentonite, gilsonite, and cementitious materialsused either without any appreciable sand or aggregate material oradmixed with a granular filling material such as sand, ground limestone,and the like.

The composition of the invention further contains a strengthening agent.The strengthening agent allows early and higher ultimate strengthdevelopment of the slurry. The strengthening agent also aids in mixingflexibility since slight changes in the water do not have such a drasticeffect on slurry properties. Such strengthening agents are typicallyfinely-divided spherical particles. Suitable as strengthening agent arefumed metal oxides and metal powder. In a preferred embodiment, thestrengthening agent is silica fume, aluminosilicate including zeolites,fly ash, alumina, aluminum metal powder, manganese oxide fume,ferro-silicon fume, wollastonite, hydrated calcium sulphoaluminate, suchas those of the formula Ca₆[Al(OH)₆]₂(SO₄)₃ 26 H₂O, salts containingsodium ions, such as sodium sulfate, sodium nitrate, sodium chloride,etc., and salts containing sulfate ions, such as calcium sulfate andpotassium sulfate, as well as mixtures thereof. Silica fume isespecially preferred. Preferably the particle size of the strengtheningagent is less than 10 microns. Even more preferably the particle size isless than 7.5 microns. The strengthening agent is typically present inan amount of from about 3 to about 20 percent by weight of cement(BWOC).

A set retarder is necessary to prevent the setting of the slurry duringstorage. The characteristics of these set retarders are diverse andimportant. An effective amount of set retarder allows the storage of theslurries with minimal changes in the characteristics of both the storedand activated slurry. It is equally important that this effect isreversible after adding an effective amount or low concentration ofactivator to the slurry, even at low well circulating temperatures. Inaddition, the set retarder should preferably provide some dispersion ofthe slurry without overdispersion, and little effect on the compressivestrength after activation and setting.

Suitable set retarders include glucoheptonates, such as sodiumglucoheptonate, calcium glucoheptonate and magnesium glucoheptonate;lignin sulfonates, such as sodium lignosulfonate and calcium sodiumlignosulfonate; gluconic acids gluconates, such as sodium gluconate,calcium gluconate and calcium sodium gluconate; phosphonates, such asthe sodium salt of EDTA phosphonic acid; sugars, such as sucrose;hydroxycarboxylic acids, such as citric acid; and the like, as well astheir blends. Calcium gluconate for hydraulic cement and slagmentslurries and sodium glucoheptonate for slag slurries are especiallypreferred.

The amount of set retarder can vary, depending on the type ofcementitious material, the type of set retarder selected and the desiredstorage time. Since this disclosure refers to liquid premixes of bothslags and hydraulic cements, the term “gpb” refers to gallons per barrelof cementitious material premix. For slagments and hydraulic cements,typical amounts of retarder range from about 0.05 gpb to 0.4 gpb,preferably from about 0.05 gpb to 0.15 gpb, with about 0.05 gpb ofretarder preferred. For slags, typical amounts of retarders range from0.05 gpb to 0.4 gpb, with about 0.075 gpb of retarder preferred.

A plasticizing agent is used in the storable slurry to assist in controlof the fluidity of the slurry. The amount of plasticizing agent dependsof the type of hydraulically-active cementitious material used, selectedsuspending agent (if required) and desired density of the storableslurry. Specific examples of plasticizing agents include melaminesulfonic acid polymer condensation product (such as “SP5”, “CORMIX”,Warrington, England), sodium polyacrylate (such as “BEVALOID 6770”,Rhone-Poulenc, Watford, England), naphthalene sulfonic acid, sodium saltof naphthalene sulfonate formaldehyde condensate, sodium sulfonatedmelamine formaldehyde (SMF) and sulfonated-styrene maleic anhydridepolymer (such as “SSMA”), (Miltemp, Milpark, Houston, Tex.). Thepreferred plasticizing agent is a sodium partially neutralizedpolyacrylate homopolymer which is commercially available from AlcoChemical as ALCOQUEST® 149.

The plasticizer should be present in amount from 0.05 gpb to 0.5 gpb.More preferably the amount should be 0.05 to 0.2 gpb, most preferablyabout 0.15 gpb.

Mixing water containing the above-mentioned additives with the dryhydraulically-active cementitious materials produces the storableslurry. A sufficient amount of water, preferably fresh water, should beadded to the hydraulically-active cementitious material to form a liquidstorable slurry of suitable consistency. A storable slurry with portlandcement should have a density measuring in the range from about 6 to 13lbm/gal and preferably in the range of about 7 to 11 lbm/gal, morepreferably about 8 to 10 lbm/gal.

Depending upon the particular storable slurry, the amount of mixingwater in the slurry of the present invention ranges from about 30 to 150weight percent based upon the dry weight of cement and preferably is inthe range of about 90 to 140 weight percent.

Additional dispersants such as polyacrylate, naphtalene sulfonic acidand the like, as well as fluid loss control agents such as hydroxyethylcellulose, acrylic copolymers, grafted tannin polymer, or similaradditives known in the art, may be added as required either to thestorable base fluid or the final activated cement slurry.

In traditional low-density cements a lightweight additive is mixed withthe cement. These additives include microspheres or a gas, such asnitrogen or compressed air. In a preferred embodiment, glass or ceramicmicrospheres are employed. Preferably, the microspheres exhibit adensity of between from about 0.25 to about 0.6, most preferably about0.35 to 0.40, g/cc and an isotatic crush resistance of from about 2000to about 18,000 psi (measured for 2 minutes in a 2 inch cell). Morepreferably the spheres are made out of borasilicate glass. Mostpreferred microspheres are commercially available from 3M and are soldunder the name Scotchlite™ Glass Bubbles HGS Series. They aremanufactured with tolerances for a specific pressure. At a givenpressure only less than 20% of the microspheres are crushed. It isnecessary therefore to first determine the amount of hydrostaticpressure that the cement will be under, and then use the microspheresdesigned for such tolerances.

The amount of microspheres used is based on the desired cement slurrydensity once placed in the wellbore and exposed to downhole pressures.Once the pressure is found, one will know which microspheres must beused based on the manufactured tolerances of the sealed microspheres.Then, the desired density must be determined. It is then possible todetermine the amount of microspheres necessary to effectuate the desireddensity as is known in the art. Typically, the microspheres are in thecomposition at a concentration of from about 20 to about 100 by weightof cement (BWOC).

Storable slurries known in the art generally require the use of asuspension agent. This is seen in U.S. Pat. No. 5,447,197. The presentinvention contains substantially no suspending agent. While somesuspending agent can be used it is preferable to have less than 0.5% byweight of water (BWOW). It has been found that the amounts of suspensionagent used in the prior art have no positive effect on the slurries ofthe present invention. In fact, when a suspending agent is used, theslurry becomes too viscous and it is more difficult to maintain fluidityas well as the activated downhole properties.

Under normal conditions, the storable slurries of the invention haveconsiderable longevity. The storable slurry of the invention shouldremain stable as a liquid, preferably for about a week and morepreferably about three to four weeks without setting. In certain cases,storage times in excess of two months can be achieved. Changes inthickening time of the activated hydraulic cement slurries, even afterprolonged storage of the non-activated slurry, are not excessive andsuch changes are readily determined and adjusted using techniques knownin the art.

At the time of cementing, the stored slurry is activated, pumped intothe well and allowed to set. Activation occurs by adding an activator orsufficient downhole temperature. The activator or downhole temperatureinitiates hydration and allows the slurry to set after a predeterminedpumping time.

The activator must counteract the set retarder while having a minimaleffect on final slurry properties or set characteristics, such asrheology and fluid loss when used in an effective amount. In addition,the activator should be easy to mix and handle, such as a liquid or drypowder; economical; widely available at reasonable purity; safe to shipand handle and environmentally acceptable.

Activators for a storable slurry include solutions of Group IA and IIAhydroxides, such as sodium hydroxide, magnesium hydroxide and calciumhydroxide; sulfates, such as sodium sulfate; aluminates, such as sodiumaluminate and potassium aluminate; carbonates, such as sodium carbonate;silicates; triethanolamine (TEA) and calcium chloride. Preferredactivators are sodium silicates. Sodium silicate has a large number ofindustrial uses which include drilling fluids and waterproofing mortarsand cements. For slag slurries a sodium silicate (“Crystal 120H”,Crosfield, Warrington, England) with a particular silica/soda ratio isespecially preferred. Sodium silicate (“Crystal 100S”, Crosfield) with adifferent silica/soda ratio is especially preferred for hydraulic cementand slagment slurries. Typical concentrations of activator range fromabout 0.05 gpb to 3.5 gpb dependent on application.

There are two approaches for controlling the thickening time of theactivated storable slurries. The first approach is to accurately meteror measure out the activator based on a dose-response curve so thestored slurry becomes “less retarded” and provides the desiredthickening time. Because the slope of the dose-response curve may besteep, the slurries may be too sensitive to permit the accurate controlof thickening at the wellsite.

The second approach is to “over-activate” the slurry and add additionalor secondary set retarders, such as lignin sulfonates, tartrates,gluconates, glucoheptonates, and the like, to achieve the desiredthickening time. The “over-activated” slurries respond normally toconventional levels of retarder and exhibit far less sensitivity. Inaddition, “over-activation” might boost the early compressive strengthof the set slurries. A typical concentration of additional set retardersodium lignosulfonate (“R12-L”, 40% active, Boregard, Sarpsborg, Norway)ranges from 0 to about 1 gpb.

EXAMPLES

This invention is demonstrated, but not limited to, the followingexamples:

In all experiments, the storable cementious slurries were made using thefollowing components:

-   -   “TXI Litewate” as lightweight oil well cement, commercially        available from Texas Industries, Dallas, Tex.;    -   gluconic acid set retarder, commercially available from BJ        Services, Houston, Tex. under the name “LSR-1”;    -   sodium partially neutralized polyacrylate homopolymer as        plasticizer;    -   sodium naphthalene sulfonate-formaldehyde copolymer as        dispersant;    -   uncompacted silica fume as strengthening agent;    -   grafted tannin polymer as fluid loss control agent; and    -   borosilicate glass microspheres, commercially available as        Scotchlite™ HGS Gas Bubbles HGS6000 from The 3M Company, having        a density of 0.46 g/cc and an isotatic crush strength of 6000        psi.

Three slurries were prepared as follows:

-   Slurry 1: Base System+Additional Dispersant+Additional Fluid Loss    Control-   Slurry 2: Base System+Additional Dispersant-   Slurry 3: Base System

The Base System comprises about 100 weight percent of TXI Litewate,about 0.8 weight percent of set retarder, about 1.7 weight percentplasticizer, about 69 weight percent of borosilicate glass microspheresand about 13 weight percent of silica fume. Slurry 2 contained anadditional 1.2 weight percent of dispersant. In addition to thedispersant, Slurry 1 contains 2 weight percent of fluid loss control.

The Base System cementitious slurry was prepared as follows. To themixwater placed in a plastic container, was added the set retarder andplasticizer which was stirred with a paddle stirrer. Once dissolved, theTXI Litewate, borosilicate glass spheres and silica fume were addedslowly to the water to avoid lumping of the cementious material. Asufficient amount of freshwater was added to reach a density of about8.1 ppg. Dispersant and fluid loss control agent were further added toSlurry 2 and Slurry 1, respectively. The resulting slurry was stirredfor about 30 minutes to ensure homogenity and dissolve any remaininglumps of dry material. The plastic container was then sealed with a lidto prevent evaporation of water from the slurry, and stored for anextended period of time. The rheology was determined and the plasticviscosity (PV) and yield point (YP) in accordance with testingprocedures outlined in API Recommended Practice 10B 22^(nd) Edition,December 1997.

At regular intervals during the storage the slurry conditions werechecked. The stability of the system as illustrated in Table 1 wasmonitored. Using a small spatula the general appearance, gellation,freewater and settling were noted. While in storage the slurry wasmaintained on a regular basis through thorough agitation with a paddlestirrer. TABLE 1 Stability of Storable Slurry Systems Slurry StorageSlurry Density Cement Retarder % Time No. ppg Type BWOW Days Comments 18.1 TXI 0.5 LSR-1  9 Stable/Viscous Litewate 2 8.1 TXI 0.5 LSR-1 15Stable Litewate 3 8.1 TXI 0.5 LSR-1 12 Stable/Gel Litewate

Rheology readings as shown in Table 2 were then taken on a daily basisto monitor the shelf life of the system. Under normal circumstances theslurry systems typically experienced a gradual increase in slurryviscosity, as well as gelling, during the storage period before itultimately reached the end of its shelf life and set hard, rendering theslurry useless. Both Fann 35 viscometer readings and the calculatedPlastic viscosity (PV) and Yield Points (YP) are displayed in Table 2.TABLE 2 Rheological Properties of Storable Base Fluid Slurry StorageBase Fluid Rheologies at Slurry Density Time 80° F. No. ppg Days600/300/200/100/6/3 PV YP 1 8.1 2 600/370/264/150/16/10 330 40 5600/396/284/166/16/10 345 51 8 600/520/392/238/32/22 423 97 2 8.1 2140/76/54/30/6/6 69 7 5 148/80/56/30/6/4 75 5 8 148/82/56/28/6/2 81 1 15162/94/66/34/6/4 90 4 3 8.1 2 112/68/54/36/16/12 48 20 5122/76/62/42/18/16 51 25 9 140/98/78/60/32/26 57 41

The activation and thickening time testing of the slurry systems wastested with three stored slurries.

-   -   Slurry 1 was constituted of 69% BWOC Scotchlite HGS 6000        borosilicate glass microspheres, 13% BWOC un-compacted silica        fume, 0.5% BWOW set retarder, 1.0% BWOW plasticizer, 1.2% BWOC        dispersant and 2.0% BWOC fluid loss additive.    -   Slurry 2 was constituted of 69% BWOC Scotchlite HGS 6000        borosilicate glass microspheres, 13% BWOC un-compacted silica        fume, 0.5% BWOW set retarder, 1.0% BWOW plasticizer, and 1.2%        BWOC dispersant.    -   Slurry 3 was constituted of 69% BWOC Scotchlite HGS 6000        borosilicate glass microspheres, 13% BWOC un-compacted silica        fume, 0.5% BWOW set retarder, 1.0% BWOW plasticizer.

The slurries were placed on an electronic scale and triethanolamine(TEA) as activator in the amount of 0.5 gpb was added. The slurry wasthen placed in a Waring blender and stirred at +/−2000 rpm forapproximately 35 seconds to ensure the full dispersion of the activatorand additives. Antifoaming agent can be employed as required to reduceor prevent air entrainment. After final activation and blending, theslurry thickening time was tested using API RP-10B procedures. Theresults of such thickening time testing are presented in Tables 3, 4,and 5 below for Slurries 1, 2 and 3, respectively: TABLE 3 Slurry 1 BaseFluid Thickening Rheologies - Cement Temperature Age of Base Time 80° F.Brand ° F. Fluid Hours PV YP TXI 225 1 Days 4:10 Litewate 225 2 Days4:10 330 40 3 Days 315 35 225 5 Days 4:00 345 51 6 Days 345 53 7 Days387 45 8 Days 423 97

TABLE 4 Slurry 2 Base Fluid Thickening Rheologies - Cement TemperatureAge of Base Time 80° F. Brand ° F. Fluid Hours PV YP TXI  1 Days 69 9TLW 225  2 Days 3:20 69 7  4 Days 72 6 225  5 Days 4:50 75 5  6 Days 722  7 Days 75 3  8 Days 81 1 11 Days 84 6 12 Days 81 5 13 Days 90 4 22514 Days 5:00 90 4

TABLE 5 Slurry 3 Base Fluid Thickening Rheologies - Cement TemperatureAge of Base Time 80° F. Brand ° F. Fluid Hours PV YP TXI  2 Days 48 20TLW 225  3 Days 3:10 51 19  4 Days 48 18  5 Days 51 25 225  6 Days 3:2054 26  9 Days 57 41 10 Days 60 46 11 Days 72 58As is illustrated in Tables 3, 4, and 5, the system demonstrated theability to obtain fundamentally equivalent thickening time underidentical downhole conditions, after being stored in a liquid state atsurface conditions for days at a time.

To confirm the compressive strength of the cured cement that hadpreviously been stored in a liquid state, test data was obtained throughAPI RP-10B destructive crush tests on samples from slurries 1 and 2measuring 2×2×2 in. After activating the slurry with 0.5 gpbtriethylamine and curing the cement at 260° F., 24 hour and 48 hourcompressive strength data as shown in Table 6 were obtained. TABLE 6Compressive Strength Data at 260° F. 24 hour Slurry Compressive 48 hourSlurry Density Cement Activator Strength Compressive No. ppg Type gpb(PSI) Strength (PSI) 1 8.1 TXI 0.5 1220 2875 Litewate TEA 2 8.1 TXI 0.5 880 1730 Litewate TEA

From the foregoing, it will be observed that numerous variations andmodifications may be effected without departing from the true spirit andscope of the novel concepts of the invention.

1. A storable, low-density, hydraulically-active, cementitious aqueousslurry comprising: (a) a hydraulically-active cementitious material; (b)a set retarder; (c) a plasticizer; (d) glass or ceramic micro-spheres;and (e) a strengthening agent; wherein the aqueous slurry issubstantially free of a suspension agent.
 2. The storable, low-density,hydraulically-active, cementitious aqueous slurry of claim 1, whereinthe set retarder is at least one member selected from the groupconsisting of hydroxycarboxylic acids, glucoheptonates, ligninsulfonates, gluconates, phosphonates, and sugars.
 3. The storable,low-density, hydraulically-active, cementitious aqueous slurry of claim1, wherein the plasticizer is at least one member selected from thegroup consisting of melamine sulfonic acid polymer, sodium polyacrylate,sodium salt of naphthalene sulfonate formaldehyde condensate, napthalenesulfonic acid polymer, and sulfonated styrene maleic anhydride polymer,or a mixture thereof.
 4. The storable, low-density,hydraulically-active, cementitious aqueous slurry of claim 3, whereinthe plasticizer is sodium partially neutralized polyacrylatehomopolymer.
 5. The storable, low-density, hydraulically-active,cementitious aqueous slurry of claim 1, wherein the glass or ceramicmicro-spheres are of a density and an amount sufficient to effectuate adensity to the storable, cementitious aqueous slurry between from about6 to about 13 lbs/gallon.
 6. The storable, low-density,hydraulically-active, cementitious aqueous slurry of claim 1, whereinthe microspheres comprise borosilicate glass.
 7. The storable,low-density, hydraulically-active, cementitious aqueous slurry of claim1, wherein the microspheres are ceramic.
 8. The storable, low-density,hydraulically-active, cementitious aqueous slurry of claim 1, whereinthe strengthening agent is at least one member selected from theconsisting of silica fume, aluminosilicate, fly ash, alumina, aluminummetal powder, manganese oxide fume, ferro-silicon fume, wollastonite,hydrated calcium sulphoaluminate, sodium sulfate, sodium nitrate, sodiumchloride, calcium sulfate or potassium sulfate.
 9. The storable,low-density, hydraulically-active, cementitious aqueous slurry of claim8, wherein the strengthening agent is silica fume.
 10. A method ofmaking a storable, low-density, hydraulically-active, cementitiousslurry which comprises the steps of: (a) adding glass or ceramicmicro-spheres to a hydraulically-active cementitious material; (b)adding a strengthening agent to the composition of (a); and (c) mixingcomposition (b) with water, a set retarder, and a plasticizer togenerate a slurry, wherein the set retarder is present in an amountsufficient to allow storage of the slurry wherein the slurry issubstantially free of a suspension agent.
 11. The method of claim 10,wherein the set retarder is at least one member selected from the groupconsisting of hydroxycarboxylic acids, glucoheptonates, ligninsulfonates, gluconates, phosphonates, and sugars.
 12. The method ofclaim 10, wherein the plasticizer is at least one member selected fromthe group consisting of melamine sulfonic acid polymer, sodiumpolyacrylate, sodium salt of naphthalene sulfonate formaldehydecondensate, napthalene sulfonic acid polymer, sulfonated styrene maleicanhydride polymer or a mixture thereof.
 13. The method of claim 12,wherein the plasticizer is sodium partially neutralized polyacrylatehomopolymer.
 14. The method of claim 10, wherein the glass or ceramicmicro-spheres are present at a density and an amount sufficient toeffectuate a density to the slurry between from about 6 to about 13lbs/gallon.
 15. The method of claim 10, wherein the glass or ceramicmicro-spheres comprise borosilicate glass.
 16. The method of claim 10,wherein the glass or ceramic micro-spheres comprise ceramic.
 17. Themethod of claim 10, wherein the strengthening agent is at least onemember selected from the group consisting of silica fume,aluminosilicate, fly ash, alumina, aluminum metal powder, manganeseoxide fume, ferro-silicon fume, wollastonite, hydrated calciumsulphoaluminate, sodium sulfate, sodium nitrate, sodium chloride,calcium sulfate or potassium sulfate.
 18. The method of claim 17,wherein the strengthening agent is silica fume.
 19. (canceled) 20.(canceled)
 21. (canceled)
 22. (canceled)
 23. (canceled)
 24. (canceled)25. (canceled)
 26. (canceled)
 27. (canceled)
 28. A storable,low-density, hydraulically-active, cementitious slurry comprising: (a) ahydraulically-active cementitious material; (b) a set retarder; (c) aplasticizer; (d) glass or ceramic micro-spheres; (e) a strengtheningagent; and (f) water wherein the slurry is substantially free of asuspension agent and further wherein the density of the slurry isbetween from about 60 to about 13 lbs/gallon.
 29. The storable, lowdensity, hydraulically-active, cementitious slurry of claim 1, whereinthe micro-spheres are borosilicate glass.